std::counted_iterator - cppreference.com (original) (raw)
std::counted_iterator is an iterator adaptor which behaves exactly like the underlying iterator, except that it keeps track of the distance to the end of its range. This iterator is equal to std::default_sentinel if and only if its count reaches zero.
Contents
- 1 Member types
- 2 Member objects
- 3 Member functions
- 4 Non-member functions
- 5 Helper classes
- 6 Example
- 7 Defect reports
- 8 See also
[edit] Member types
| Member type | Definition |
|---|---|
| iterator_type | I |
| value_type(conditionally present) | std::iter_value_t<I> if I models indirectly_readable; otherwise, not defined |
| difference_type | std::iter_difference_t<I> |
| iterator_concept(conditionally present) | I::iterator_concept if present; otherwise, not defined |
| iterator_category(conditionally present) | I::iterator_category if present; otherwise, not defined |
[edit] Member objects
| Member name | Definition |
|---|---|
| current (private) | the underlying iterator which base() accesses(exposition-only member object*) |
| length (private) | the distance between the underlying iterator and the end of its range(exposition-only member object*) |
[edit] Member functions
| (constructor) | constructs a new counted_iterator (public member function) [edit] |
|---|---|
| operator= | assigns another counted_iterator (public member function) [edit] |
| base | accesses the underlying iterator (public member function) [edit] |
| count | returns the distance to the end (public member function) [edit] |
| operator*operator-> | accesses the pointed-to element (public member function) [edit] |
| operator[] | accesses an element by index (public member function) [edit] |
| operator++operator++(int)operator+=operator+operator--operator--(int)operator-=operator- | advances or decrements the counted_iterator (public member function) [edit] |
[edit] Non-member functions
| operator==operator<=>(C++20) | compares the distances to the end (function template) [edit] |
|---|---|
| operator==(std::default_sentinel)(C++20) | checks if the distance to the end is equal to 0 (function template) [edit] |
| operator+(C++20) | advances the iterator (function template) [edit] |
| operator-(C++20) | computes the distance between two iterator adaptors (function template) [edit] |
| operator-(std::default_sentinel_t)(C++20) | computes the signed distance to the end (function template) [edit] |
| iter_move(C++20) | casts the result of dereferencing the underlying iterator to its associated rvalue reference type (function) [edit] |
| iter_swap(C++20) | swaps the objects pointed to by two underlying iterators (function template) [edit] |
[edit] Helper classes
[edit] Example
#include #include #include #include #include using std::operator""s; void print(auto const remark, auto const& v) { const auto size = std::ssize(v); std::cout << remark << '[' << size << "] { "; for (auto it = std::counted_iterator{std::cbegin(v), size}; it != std::default_sentinel; ++it) std::cout << *it << (it.count() > 1 ? ", " : " "); std::cout << "}\n"; } int main() { const auto src = {"Arcturus"s, "Betelgeuse"s, "Canopus"s, "Deneb"s, "Elnath"s}; print("src", src); std::vector<decltype(src)::value_type> dst; std::ranges::copy(std::counted_iterator{src.begin(), 3}, std::default_sentinel, std::back_inserter(dst)); print("dst", dst); }
Output:
src[5] { Arcturus, Betelgeuse, Canopus, Deneb, Elnath } dst[3] { Arcturus, Betelgeuse, Canopus }
[edit] Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| P2259R1 | C++20 | member typedefs are not provided std::incrementable_traitsis specialized for counted_iterator | member typedefs are added to account for iterator_traits fixredundant std::incrementable_traits specialization is removed |